The present invention relates to a cam phaser apparatus for controllably varying the phase relationship between the crankshaft and the camshaft of an internal combustion engine; more particularly, to a cam phaser having concentric splined elements counter-rotatable by a splined piston therebetween; and most particularly, to a splined cam phaser wherein the parts are optimized for ease and economy of manufacture, reduced phaser size, and improved phaser performance.
Splined cam phasers are well known in the automotive art; see, for example, US Pat. Ser. No. 5,588,404. In principle, a phaser assembly is relatively simple. A first rotatable element is fixedly mounted to the end of a camshaft of an engine and turns synchronously therewith. The first element has helical splines on its outer surface. A second rotatable element surrounds the first element concentrically and has a drive wheel, pulley, or sprocket adapted to be driven by the crankshaft of the engine. On its inner surface, the second element has helical splines opposite-handed from the splines on the first element. A generally cylindrical piston is positioned in a closed annular space between the two elements. The piston has helical splines on both its inner surface and its outer surface which mesh with the splines on the first and second elements. The piston is controllably driven axially in either direction by programmably-directed hydraulic pressure against one or the other side of the piston, causing the first and second elements to counter-rotate with respect to each other and thereby varying the relative timing of the valves with respect to the pistons by changing the rotational phase relationship between the crankshaft and the camshaft. Preferably, the first element is provided at its outer end with a sectored timing wheel, also referred to herein as a target wheel, to permit automatic monitoring of the cam position at all times.
The prior art cam phaser can be difficult and expensive to manufacture. Typically, all moving parts are individually machined from steel forgings. The target wheel, which carries the compressive force of the major assembly bolt, is optimally formed by investment casting, a very expensive forming method. The layout of the parts and seals does not lend itself to formation by less expensive known methods, for example, by powdered metal forming, preferably by powdered steel. Further, the internal passages in various parts, required to present hydraulic fluid to one or the other face of the piston, typically are formed labor-intensively by cutting and drilling.
Therefore, what is needed in the art is an improved splined cam phaser wherein the cost of manufacture is minimized by minimizing the number of machined parts. Still further needed in the art is an improved splined cam phaser wherein the speed of response is improved.
Briefly described, an improved splined cam phaser in accordance with the invention comprises four assemblies: a sprocket assembly, an inner hub assembly, a cover assembly, and a piston assembly. The joined assemblies provide an improved phaser function over that of the prior art phaser. The component parts of the assemblies are re-configured from the analogous parts of the prior art phaser to permit much of the improved phaser to be manufactured inexpensively by powdered metal forming or by stamping from sheet metal, in contrast with a prior art cam phaser wherein all parts are formed expensively either by machining from forged blanks or by investment casting. These changes reduce the cost of manufacture, reduce the weight and axial length, and improve the speed of response, all of which are important customer acceptance criteria. In addition, the irregularly shaped and larger capacity oil passages of the present invention, which require no machining after forming, permit further improvement in speed of response time of the phaser assembly. Further, the proportions of some parts are altered such that all radial and axial loads are borne by a single bearing rather than two bearings as in the prior art phaser, thereby reducing variability in axial alignment of the component parts.
The present invention overcomes the problems of the prior art by providing a cam phaser with a lighter, less expensive sheet metal cover. The invention can use a sheet metal cover to replace the conventional cast and machined cover by rearranging the load distribution of the cam phaser. Instead of the cover bearing the load, the invention places the load on an inner hub. With the load redistributed, the cover is made with less expensive materials and processes. In the preferred embodiment, the cover is made of sheet metal or net casting. The cover, while providing a seal for the pressure chamber that actuates the piston, no longer bears the load of the camshaft. A target wheel, also of sheet metal, is an optional component that is mounted on the outside of the cover. The target wheel has indicia for generating signals representative of the angular position of the cam phaser. Those signals are used to control the setting of the angle of the cam phaser.
With the present invention all the components of the cover and the inner hub are net shaped as originally manufactured thereby eliminating the cost of additional machining. The added machining of o-ring grooves is also eliminated. Likewise, targets are net cast into the sheet metal cover or are easily stamped rather than machined into a cast cover.
Further, with the present invention the manufacturing of the piston is simplified and the cost reduced by eliminating the need to machine grooves for the seals in the piston skirt.